A broad area of mid to upper level high pressure anchored over West will keep temperatures above seasonal average across the Interior Northwest.
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Daily maximums are forecast to climb into the mid-upper 90s across the Northwest and into the some areas across the High Plains.
Most of the threat for heat stress has relaxed, but a small area across southeast Montana/northeast Wyoming has a Heat Advisory in effect through tonight.
The warm weather and gusty winds will support an Elevated fire weather risk tomorrow across portions of the Interior Northwest and along the Montana Hi-Line, per the Storm Prediction Center.
There are scattered areas with Red Flag Warnings across western Washington, Oregon, northeast California and northeast Montana.
Meanwhile, cooler temperatures are beginning to filter into the Great Lakes and Northeast today and will continue through Thursday as a slow moving cold front sinks south across the Interior Northeast into the Upper Mississippi Valley.
Much of the East will have another day of the heat before temperatures start to moderate to around average, before a secondary cold front in Canada brings a reinforcing shot of cool air into the region by the end of the work week.
Excessive heat is no longer a threat across the Northeast.
Along with the change in temperature, this frontal boundary will be the focus for scattered to widespread showers and thunderstorms that will increase the threat for heavy rainfall and flash flooding from the Mississippi Valley to the Central Appalachians; these locations have been very wet the last few weeks, so it would not take much rain to cause flash flooding.
WPC is maintaining a Slight Risk (level 2/4) of Excessive Rainfall across the Gulf Coast, Mississippi Valley and into the Central Appalachians/Mid-Atlantic region through Thursday morning with lingering rainfall and elevated risk (Marginal) into Friday morning for the Appalachians and the Gulf Coast through Saturday morning.
Shifting focus over the west, the upper ridge will continue to allow monsoonal moisture to pump northward from the Southwest into the Great Basin and Interior West.
Diurnal heating along with the over abundant moisture will help trigger widespread scattered monsoonal showers and thunderstorms across these areas over the next few days.
Isolated flash flooding is possible across these areas, especially over burn scars, slot canyons, dry river beds or urban areas.
WPC has Slight Risks in effect through Saturday morning.
The Southeast quarter of the Lower 48 will also hold in a stagnant, wet pattern.
The frontal boundary pressing into the Ohio Valley and Northeast will not make much headway south through this week, keeping the Southeast in the warm sector through Thursday.
As such, expect widespread showers and thunderstorms in the region, where portions of the Lower Mississippi Valley and Central Gulf Coast have the best chances for heavy rains.
The clouds and rain across this area will also keep high temperatures over the next few days slightly below average. ■
A clipper system will move quickly across the northern Plains into the Midwest Friday and the Northeast by Saturday, bringing a wintry mix of rain and snow showers ahead of a sweeping cold front.